WO2013175099A1

WO2013175099A1 - Self-compressing osteosynthesis screw

Info

Publication number: WO2013175099A1
Application number: PCT/FR2013/051051
Authority: WO
Inventors: Guillaume Derouet
Original assignee: Neosteo
Priority date: 2012-05-21
Filing date: 2013-05-14
Publication date: 2013-11-28
Also published as: FR2990618A1; FR2990618B1

Abstract

A self-compressing osteosynthesis screw, embodied in the form of a longitudinal body with axis A comprising, between the free distal and proximal ends of same: -a distal thread (1) with pitch (P1), the root (14) of the distal thread (1) defining a cone-shaped body, -a head thread (2) with pitch (P2) less than the pitch (P1) of the distal thread, -an intermediate smooth portion (3) connecting the distal thread (1) to the head thread (2), -a longitudinal through-hole, The root (24) of the head thread and the crest (23) of the head thread each defining, from the free distal end towards the free proximal end of the screw, a bulging body that is extended by a body cylindrical in shape, said bulging bodies, one of which is defined by the crest (23) of the head thread, the other by the root (24) of the head thread, having respectively a distance between the crest (23) and axis A of the screw, and a distance between the root (24) and axis A, which increase when axis A is followed moving towards the proximal free end.

Description

AUTOCOMPRESSIVE SCREW OF OSTEOSYNTHESIS

The field of the invention is that of the design and manufacture of osteosynthesis equipment. More specifically, the invention relates to a self-compressing screw, term by which is meant a threaded rod, intended to secure two bones or fragments of bone between them by exerting a compressive force tending to press them against each other.

Such a screw is used in orthopedic surgery, in operations to repair fractures appeared in particular in very small bones, such as in the foot or hand.

It is installed in the body of the patient, in a direction generally oblique to the axis of the fracture, so that its maintenance in each of the two ends of bone is sufficient for them to be firmly held tight. one against the other.

To facilitate and secure the insertion of the screw in the desired direction, a guide pin diameter smaller than the nominal diameter of the screw is, in general, introduced before the screw. This limits the risk of the screw being skewed or sheared and deformed. This also favors the realization of small screws.

According to a conventional embodiment, a self-compressing screw for osteosynthesis is therefore in the form of a longitudinal body of axis A of the type comprising between its distal and proximal free ends:

a distal thread of pitch, the bottom thread of the distal thread defining a conical shaped body,

a head or proximal thread with a pitch smaller than the pitch of the distal thread; an intermediate smooth part connecting the distal thread to the head thread;

- A longitudinal through hole for sliding the screw on a guide pin previously introduced into the bones or bone fragments to bring together.

An issue in the production of such screws is to optimize their support and support capacity in both ends of the bone, while minimizing their size and the implantation trauma generated in the patient.

Note that the head thread of such a screw has, conventionally, a bottom of a thread and a ridge defining a cylindrical or conical shape. However, several disadvantages have appeared when using the screws of the prior art, among which:

the compression of the two bone or bone fragments made with these screws is not optimal, loosening may appear in the long between the bone fragments;

- The screws have a head too invasive and have protruding elements, especially given their oblique mounting and their cylindrical or conical head, may cause pain for the patient; removal of the screws after bone consolidation is sometimes extremely difficult, if not impossible, and at least requires specific means, such as an ablation kit;

the connection between the head and the rest of the body of these screws is fragile, to the point that it sometimes breaks when subjected to the efforts of introduction into the bone or removal of the bone. The invention particularly aims to overcome these disadvantages of the prior art.

More specifically, the invention aims to provide a self-compressing screw osteosynthesis offering better compression between bone fragments, in terms of strength and durability.

The invention also aims to provide such a screw which is less invasive and less traumatic for the patient.

Another object of the invention is to allow the removal of such screws, after tightening, without additional means.

The invention also aims to provide such a self-compressing screw which is less subject to the risk of deformation and rupture.

These objectives, as well as others which will appear later, are achieved thanks to the invention which has for object a self-compressing screw of osteosynthesis in the form of a longitudinal body of axis A of the type comprising between its ends distal and proximal free:

a head or proximal thread with a pitch smaller than the pitch of the distal thread,

an intermediate smooth portion connecting the distal thread to the head thread,

a longitudinal through orifice,

characterized in that the thread root of the head thread and the ridge of the head thread each define, from the distal free end towards the proximal free end of the screw, a domed body extending through a body of cylindrical form, these curved body defined one, by the crest of the head thread, the other by the thread bottom of the head thread respectively having one, a distance between the ridge and the axis A of the screw and the other, a distance between the bottom of the thread and the axis A which increase when following the axis A towards the proximal free end.

In this way, compression made between two pieces of bone can be optimized using a screw whose head has limited protruding forms. The screw is then completely embedded in the bone, which limits the risk of external interference, loosening, or even breaking in the connection between the head and the rest of the body of the screw. A screw having this head shape is also less intrusive and less offensive than a cylindrical or conical screw head, as performed according to the prior art. In addition, the domed shape of the head thread, both at the bottom of the thread and at the crest of the net, allows to achieve a smooth tightening effort in the bone, without compromising the possibility of removing the screw after tightening. The screw is thus preserved, its rounded shapes make it less sensitive to the efforts tending to cause it to break, and the same tools (known per se) can then be used to install and uninstall the screw in the bone.

Advantageously, the peak of the distal thread defines, from the distal free end towards the proximal free end of the screw, a body of cylindro-conical shape or of conical shape with two cones opposed by their base.

In other words, the peak of the distal thread defines from the distal free end of the screw is a first conically shaped body whose diameter increases from the distal free end towards the proximal free end of the screw followed a second conically shaped body whose diameter decreases from the distal free end towards the proximal free end of the screw, or a cylindrical body followed by a conical body whose diameter decreases from the distal free end towards the proximal free end of the screw.

Thanks to this characteristic, conical in shape with two cones opposed by their base of the crest of the distal thread, the introduction of the screw into the bone allows a progressive tightening, and the removal of a tight screw in the bone is ease. Preferably, when the peak of the distal thread defines from the distal free end of the screw a first conically shaped body whose diameter increases from the distal free end towards the proximal free end of the screw followed by a second conically shaped body whose diameter decreases from the distal free end towards the proximal free end of the screw, the taper angle of the first body is greater than or equal to the taper angle of the second body. The angle of taper of the first body, or respectively of the second body, is defined by the angle formed between the axis A of the longitudinal body of the screw and the straight line passing through the crest of the distal thread of the first body or the second body respectively. body.

Preferably, the distance between the ridge and the axis A of the screw of the curved body defined by the crest of the head thread increases faster than the distance between the bottom of the thread and the axis A of the curved body. defined by the thread root of the head thread when following the axis A towards the proximal free end. This design facilitates the implantation of the screw into the bone. According to an advantageous solution, the threads of the distal thread and the head thread each have an inclined profile, the inclined profile of the distal thread being oriented in a direction opposite to the inclined profile of the head thread.

This feature optimizes the support and retention of the two threads in the respective bone or bone fragment to which they are intended to be joined, and further improves the compression of the two ends of bone against each other.

Preferably, the proximal free end of the screw is chamfered. The presence of a chamfer makes it possible to limit the overflow of the screw head out of the bone without affecting either the installation or removal of the screw.

Preferably, the peak of the head thread and the peak of the distal thread have a flat top. This design facilitates the penetration of the screw and its removal from the bone.

Preferably, the osteosynthesis screw has a head with six internal lobes or hexagon socket. A tool known per se (for example an allen key or torx - registered trademarks) can thus be used to tighten the screw in the bones, tighten the pieces of bone against each other, and then loosen the assembly optionally.

Advantageously, the osteosynthesis screw is self-tapping. Thus, the mounting of the screw in the bone or bone fragments does not require their prior tapping. The insertion of a guide pin, on which the screw is paved to slide, is a sufficient preparation to allow the fastening of the screw on the bone.

According to a preferred solution, the osteosynthesis screw contains titanium. This material makes it possible to produce a screw which, by virtue of its properties of mechanical strength, machinability and acceptance by the human body, is perfectly suited to the osteosynthesis applications concerned.

Other characteristics and advantages of the invention will emerge more clearly on reading the following description of a preferred embodiment of the invention, given by way of illustrative and nonlimiting example, and the appended drawings among which:

Figure 1 is a longitudinal view of a screw according to the invention, comprising a dotted representation of the hidden parts;

Figure 2 is a view of a distal thread according to Figure 1, specifying the shape defined by the thread bottom;

FIG. 3 is a view of a head thread according to FIG. 1, specifying the shape defined by the ridge and the thread root;

Figure 4 is an axial view of the head of a screw according to Figure 1;

Figure 5 is a longitudinal view of a screw according to the invention, after rotation of 90 ° about its axis with respect to its representation in Figure 1;

Figure 6 is a perspective view of the screw according to Figure 1;

FIG. 7 is a schematic representation of the curved shape of the head of a screw according to the invention;

FIGS. 8A and 8B illustrate the proximal free end of a screw without chamfer (FIG. 8A) and with chamfer (FIG. 8B);

Figure 9 illustrates the view of a screw with the detail of the inclined profiles of the distal and head threads.

As indicated above, the principle of the invention consists in proposing a self-compressing screw for osteosynthesis, comprising a head having a thread whose ridge and the thread base describe from the distal free end toward the free end proximal of the screw a convex shape followed by a cylindrical shape.

With reference to FIG. 1, a screw according to the invention comprises:

a distal thread 1, intended to pass through a first bone or fragment of bone, then to penetrate a second bone or fragment of bone, with a view to anchoring the screw in the latter;

a head thread 2, intended to anchor the screw in the first bone or fragment of bone, while allowing the latter to be brought closer to the second bone or bone fragment;

- A smooth part 3 intermediate, connecting the head threads to the distal thread;

a longitudinal orifice 4 passing through the screw from one side to the other.

Such a screw, intended in particular for use in surgery of the foot or hand (osteotomy operation ...), has a section whose dimensions are of the order of a millimeter, and a length that can reach a few tens millimeters.

The screw is made of a material containing in particular titanium.

According to the principle of the invention, and as shown in solid lines in FIG. 3, the ridge 23 and the thread root 24 of the head thread 2 each define a body convex shape followed by a cylindrical body.

More specifically, the distance between the crest 23 of the head thread 2 and the axis A of the screw, as well as the distance between the thread root 24 of the head thread 2 and the axis A, increase during a progression. along the axis A towards the end of the screw head. This increase, greater for the ridge 23 than for the bottom of the net 24, evolves in both cases less and less quickly, to the point that the ridge and the bottom of the net are practically at a constant distance from the axis A to approaching the end of the screw head to impart to said body a cylindrical shape.

The clamping force of the head thread 2 in the bone, at the end of the stroke of the screw, can therefore be kept very close to a desired minimum value, which makes it possible not to compromise the loosening and removal of the opinion.

On the other hand, this domed shape, produced by machining, gives the head thread 2 a less protruding profile than the V-shaped profile of the conventional screws, the ridge 23 being truncated ("clipped" or "flattened"). The curved profile of the head thread 2, both at the level of the ridge 23 and the thread root 24, thus minimizes the sharp edges of the screw, likely to project relative to the bone in which it is clamped, and it facilitates its disassembly.

As illustrated, the distal thread 1 has, from the distal free end, a thread root 14 which defines a conical shaped body. The ridge 13 of the distal thread 1 defines a conically shaped body with two cones opposite from their base, from the distal end toward the proximal end of the screw. The peak of the distal thread 1 thus defines in the vicinity of the intermediate smooth portion 3 a cone of increasing diameter towards the distal free end which facilitates the withdrawal of the screw.

Generally, the taper angle of the first body is greater than or equal to the taper angle of the second body. Thus, in the examples shown, the taper angle of the first body is close to 3 ° while the taper angle of the second body is close to 2 °. The peak 13 of the distal thread has a maximum diameter D1 (nominal diameter of the distal thread).

The cone defined by the thread bottom 14 of the distal thread has a diameter which increases during a progression along the axis A towards the end of the screw head. The angle a between the surface of this cone and the axis A is of the order of degree.

Note that, in the illustrated embodiment, the peak 13 has a truncated V profile or "flattened", the thickness increases when following the axis A towards the end of the screw head.

To allow tightening of the head thread 2 in the first bone or bone fragment, previously traversed by the distal thread 1, the nominal diameter D1 of the distal thread 1 is smaller than the maximum diameter D2 reached by the ridge 23 of the head thread. 2 at the end of the screw head.

More precisely, in the illustrated embodiment, D1 is close to the maximum diameter d2 reached by the thread root 24 of the head thread 2.

In addition, the distal threading 1 has two threads January 1 and 12 imbricated, so that it has an apparent pitch, constant, noted P1. The head thread 2 also has two threads 21 and 22 nested, so that it has an apparent pitch, constant, noted P2. The approximation between the bones or fragments of bone is allowed by the fact that P1 is greater than P2. Indeed, during the mounting of the screw, the advance of the distal thread 1 in the second bone or bone fragment is then faster than the advance of the head thread in the first bone or bone fragment, which mechanically engenders a reduction of the game separating them. Note that the distal thread 1 and the head thread 2 could equally well, and independently of one another, have a single thread, or more than two threads nested within each other.

The approximation and the compression of the two bones or fragments of bone against each other is facilitated by the presence of the smooth part 3, which separates the distal thread 1 from the head thread 2, so that these threads come into contact with each other. anchor respectively in only one of the two ends of bone, without possible interference with another bone fragment, until the tight position is reached.

The smooth part 3 takes the form of a cylinder of diameter D3, which corresponds to the maximum diameter of the cone defined by the thread root 14 and to the minimum diameter of the convex body defined by the bottom of the net 24. It thus ensures a continuity between the distal thread 1 and the head thread 2, which reduces the risk of rupture between these different parts.

FIG. 5 and FIG. 9 illustrate that the thread profiles of the threads 1 and 2 are not symmetrical but generally inclined with respect to a plane perpendicular to the axis A of the screw. More precisely, the inclined profile X1 of the distal thread 1 is, in the illustration of FIG. 5, oriented in a direction opposite to the inclined profile X2 of the head thread 2. Indeed, by moving along the axis A , the profile of the thread of the distal thread 1 is ascending between the thread root 14 and the ridge 13 when moving towards the end of the screw head, while the thread profile of the head thread 2 is ascending between the thread root 24 and the ridge 23 when advancing from the end of the screw head, so in the opposite direction.

This opposition between the inclination of the profiles of the two threads 1 and 2 increases the clamping force and retention between the two bones or bone fragments in which they are mounted.

Moreover, the orifice 4 comprises a cylindrical portion 41 of diameter D4 constant, extending inside the distal thread 1 and the smooth portion 3, and flaring towards a recess 42 whose section is provided to receive a screwing tool of complementary shape. The cylindrical portion 41 allows the screw to slide on a guide pin (not shown) previously inserted into the bone or bone fragments, to optimize the positioning of the screw, as it is introduced. The screwing tool used for this, known per se and not shown, generally has a portion of cooperation with the recess 42, intended to transmit the clamping force exerted by the surgeon, as it is itself traversed by an orifice whose diameter is at least equal to D4, to allow the sliding of the tool on the spindle.

According to one embodiment, illustrated in Figures 4 and 6, the recess 42 has a hexagon socket section or "torx" (registered trademark).

Of course, the head of the screw may have a recess 42 characterized by other shapes may correspond to a screwing tool: six-lobe internal head, in particular.

Note that the smooth cylindrical portion 3, the cylindrical portion 41 and the recess 42 are also centered on the axis A of the screw and the threads 1 and 2.

Such a screw, entirely traversed by the longitudinal orifice 4, is also called cannulated screw.

According to a preferred embodiment, the distal thread 1 and the head thread 2 are, at least for one of them, provided for tapping the bone or bone fragment to which they must be secured.

Thus, the bone does not need to be pre-drilled and tapped in order to receive the screw, and a guide pin can be inserted then securely. kept in the bone when the screw is inserted. Such a screw, self-tapping, thus simplifies, to make reliable the surgical operation and to reduce its duration. Figure 7 schematically illustrates the head of a screw according to the invention.

As illustrated, the envelope 230 defined by the peak 23 of the screw head has a curved shape whose radius of curvature R1 is between 2.5 mm. The envelope 240 defined by the thread root 24 of the screw head has a convex shape whose radius of curvature R2 is between 2.73 mm and 12 mm.

In the vicinity of the free end of the screw head, the envelopes 230 and 240 have a cylindrical shape. The free end of the screw head still called proximal free end is chamfered. The bevel shown in FIGS. 5 limits the overflow of the specimen head out of the bone as shown in FIG. 8B compared to FIG. 8A showing a chamfer-free screw head.

Claims

1. Self-compressing screw for osteosynthesis, in the form of a longitudinal body of axis A of the type comprising between its distal and proximal free ends:

a distal thread (1) of pitch (P1), the thread root (14) of the distal thread (1) defining a conical body,

a head (2) or proximal pitch thread (P2) smaller than the pitch (P1) of the distal thread,

a smooth part (3) intermediate connecting the distal thread (1) to the head thread (2),

a through longitudinal orifice (4),

characterized in that the thread root (24) of the head thread and the ridge (23) of the head thread each define, from the distal free end towards the proximal free end of the screw, a shaped body convex body extending through a body of cylindrical shape, these curved body defined one by the peak (23) of the head thread, the other by the thread bottom (24) of the head thread respectively having the one, a distance between the crest (23) and the axis A of the screw and the other, a distance between the bottom of the thread (24) and the axis A which increases when one follows the axis A in direction of the proximal free end.

2. Osteosynthesis screw according to claim 1, characterized in that the peak (13) of the distal thread (1) defines, from the distal free end towards the proximal free end of the screw, a shaped body cylindro-conical or conical in shape with two cones opposed by their base.

3. Osteosynthesis screw according to any one of claims 1 or 2, characterized in that the distance between the ridge (23) and the axis A of the screw of the convex body defined by the crest (23) of the head thread increases faster than the distance between the thread root (24) and the axis A of the curved body defined by the thread root (24) of the head thread when following the axis A in direction of the proximal free end.

4. Osteosynthesis screw according to any one of claims 1 to 3, characterized in that the threads of the distal thread (1) and the head thread (2) each have an inclined profile, the inclined profile (X1) of the distal thread being oriented in a direction opposite to the inclined profile (X2) of the head thread.

5. Osteosynthesis screw according to any one of claims 1 to 4, characterized in that the proximal free end of the screw is chamfered.

6. Osteosynthesis screw according to any one of claims 1 to 5, characterized in that the ridge (23) of the head thread (2) and the ridge (13) of the distal thread (1) have a flat top.

7. screw osteosynthesis according to any one of claims 1 to 6, characterized in that it has a six-lobe internal head or hexagon socket.

8. Osteosynthesis screw according to any one of claims 1 to 7, characterized in that it is self-tapping.

9. Osteosynthesis screw according to any one of claims 1 to 8, characterized in that it contains titanium.